High frequency performance of Si(1-x)Ge(x)/Si(1-y)Ge(y)/Si(1-x)Ge(x) HBTs

The results of a theoretical study of the performance of high speed SiGe HBTs is presented. The study includes a group of SiGe HBTs in which the Ge concentration in the base is 20 percent higher than that in the emitter and collector (i.e., y = x + 0.2). It is shown that the composition dependences of f(T) and the f(max) are nonmonotonic. As the Ge composition in the emitter and collector layers is increased, f(T) and f(max) first decrease, then remain constant and finally increase to attain their highest values.